Circuit for producing a localized nonlinearity in a generally linear voltage transfer characteristic



Feb. 10, 1959 W. W. MOE CIRCUIT FOR PRODUCING A LOCALIZED NON-LINEARITY IN A GENERALLY LINEAR VOLTAGE TRANSFER CHARACTERISTIC Filed May 28, 1955 OUTPUT VOLTAGE o INPUT V0 LTAGE.

FIGJA.

INVENTOR. WILLIAM -WEST MOE HIS ATTORNEYS.

United States Patent T CIRCUIT FOR PRODUCING A LOCALIZED NON- LINEARITY IN A GENERALLY LINEAR VOLT- AGE TRANSFER CHARACTERISTIC William West Moe, Stratford, Conn., assignor to Time, IYIICOI'POI'ItCd, New York, N. Y., a corporation of New ork Application May 28, 1953, Serial No. 358,154

4 Claims. (Cl. 250-27) The present invention relates to an electronic control device and more particularly to an auxiliary control circuit for producing nonlinearities in otherwise linear characteristics.

It is often desirable to produce predetermined distortion or nonlinearity in the characteristic curves of voltages or currents utilized in the control of electronic equipment. For example, it is sometimes desirable for the current through a glow lamp, when used in combination with photoelectric devices and the like, to have a substantially linear characteristic with respect to the input control voltage for a large portion of its operating range and at the same time to have dips or depressions inserted at particular points on the characteristic curve. Conventional nonlinear control circuits could be utilized to produce variations in the input voltage characteristics to such a device. However, when such variations are made in a linear characteristic, the

portions of the curve subsequent to such variations are not returned to coincidence with an extension of a linear portion of the characteristic prior to the variations. This usually results from the fact that, when the various control tubes either reach saturation or their cut-off value, they remain in that condition. Thus the portion of the characteristic subsequent to variation is permanently displaced from coincidence with an extension of a linear portion preceding the variation.

It is an object of the invention, accordingly, to provide a nonlinear control circuit which will overcome this disparity between the linear portions of a control char- 1 acteristic.

In accordance with the invention, an auxiliary electronic control circuit produces a voltage drop across a voltage limiting means, which is placed in series with an otherwise linear voltage control circuit, during a portion of a linearly increasing or decreasing voltage input to said voltage control circuit. This voltage drop in the otherwise linear circuit produces a dip or depression in the resultant voltage characteristic of the circuit.

For a better understanding of the invention reference should be made to the following detailed description taken in conjunction with the accompanying figures of the drawing, in which:

Fig. 1 is a schematic diagram of an electronic nonlinear control circuit, in accordance with the invention; and

Fig. 1A is a characteristic curve showing a conventional linear input voltage characteristic with a dip or depression impressed thereon, in accordance with the invention.

Referring now to the schematic diagram of Fig. 1, a conventional electron discharge device 10 having a control element 11, a plate 12 and a cathode 13 is shown. The energizing circuit for the electron discharge device 10 may include a plate load resistor 15 and a cathode biasing resistor 16. A source of linearly varying voltage may be connected to input terminals 17 and 18 with a nonlinear control circuit interposed between the terminal 2,873,362 Patented Feb. 10, 1959 the terminal 22 by the conductors 20 and 21, respectively. Two auxiliary control tubes 24 and 25 may also be connected between the terminal 17 and the terminal 22. A control grid 26 of the electron tube 24 is connected by a conductor 27 to the input terminal 17, through the conductor 20. The tube 24 may be energized from a conventional D. C. voltage source through the plate load resistor 28 connected to a plate 29, with a source 30 of biasing potential, for example a battery and a potentiometer, and a cathode biasing resistor 30a connected in series between a cathode 31 and a ground or reference point 32.

A voltage divider 34 comprising resistances 34a and 34b may be connected between a reference point 35 and the low voltage side of the plate load resistor 28, through a conductor 36. A control grid 38 of the electron tube 25 may be connected to a junction point 39 on the voltage divider 34. The electron tube 25 may have cathode 40 connected by a source 41 of biasing potential, for example a battery and a potentiometer, and a cathode biasing resistor' 41a to a reference point or ground 42. A plate 44 of the electron tube 25 may be directly connected by a conductor 45 to terminal 22 on the conductor 21 between the voltage dropping resistor 19 and the control element 11 of the electron discharge device 10. The sources of biasing potential 30 and 41 may be adjusted to provide any suitable predetermined fixed biasing potential.

The operation of the control circuit of Fig. 1 may be understood by reference to the characteristic curve shown in Fig. 1A. The source of biasing potential 41 may be adjusted so that the tube 25 will become conductive when a predetermined positive voltage, for example 50 volts, corresponding to the point P in Fig. 1A, is applied to the plate 44. The source of biasing potential 30 may be adjusted so that the tube 24 becomes conductive when the voltage applied to the grid 26 exceeds a predetermined voltage, for example 60 volts, corresponding to a point intermediate the points P and P in Fig. 1A. A linearly increasing source of voltage is connected to the terminal 17.

Thus as the input voltage applied at the terminal 17 increases from zero volts to the point P in Fig. 1A, in this case 50 volts, there is no potential drop across the resistance19 since both the tubes 24 and 25 are nonconducting. This increase in input voltage produces a linearly increasing output current across the plate load resistor 15 of the electron discharge device 10, assuming that the tube characteristic of the discharge device 10 is linear in that range. When the input voltage reaches the value corresponding to the point P the tube 25 begins to draw current. This produces a. voltage drop across the resistance 19, thereby introducing a nonlinearity into the input circuit. As the input voltage continues to increase past the point P the characteristic curve of the voltage applied to the control element 11 is flattened by the action of the dropping resistor 19, thereby producing a corresponding flattening of the output current across the resistor 15. When the input voltage applied to the terminal 17' reaches a value corresponding to a point intermediate the points P and P on the curve of Fig. 1A, in this case 60 volts, the tube 24 begins to conduct. This produces an increased voltage drop across the plate load resistor 28 and thereby decreases the voltage drop across the voltage divider 34 and consequently the voltage applied to the grid 38 of the tube 25. As the input voltage to the terminal 17 continues to increase, the voltage on the grid 38 becomes more and more negative' and acts to decrease even more the current flow through the tube '25, thereby continuously lessening the voltage drop across the resistor 19. When the input voltage at the terminal 17 reaches a value corresponding to the point P for example 70 volts, the tube .25 is rendered non-conductive, thereby eliminating the current flow through the dropping resistor 19.

' Thus the circuit provides for a linear response in the limited region from zero to P with a nonlinear response from P to P and a restoration of the linearityabove P 'It will he understood that the above embodiment is rnerely exemplary and that it is susceptible of modification and change Without departing from the spirit and scope of the invention. For example, any conventional form of biasing circuit which will produce a fixed bias can be utilized to control the bias of the tubes 24 and 25 [as an alternative to the sources of biasing potential 30 and '41. The auxiliary control tubes may be tetrodes, pentodes, or any other suitable types of tubes, instead of triodes as shown. Further, it will be obvious to those skilled in the art that the electron discharge device It 'With its associated plate load resistor 15, is merely part of the exemplary embodiment of the invention and that any suitable utilization device may be substituted therefor. Thus the invention is deemed to be limited only by the appended claims.

I claim: 1. A control circuit for producing a localized nonlinearity between a first and second potential in an otheracross-said resistance" meansg-and-rnea'ns connected to said input terminal and responsive to said input voltage source to render said signal translating means nonconductive, thereby to eliminate said voltage drop.

2. A control circuit as set forth in claim 1 wherein said signal translating means comprises an electron discharge device having at least a plate, a cathode and a control element. 7

3. A control circuit as set forth in claim 2 wherein said means connected to said input terminal and responsive to said input voltage source comprises a second signal translating means having at least a control element and a'plate, said control element of said second signal translating means being connected to said input terminal of said resistance means, circuit means connecting said plate of said second signal translating means to said control element of said one signal translating means and means for biasing said second signal translating means to become conductive in response to said input voltage source so that said one signal translating means becomes nonconductive at said second potential.

4. A control circuit as set forth in claim 3 wherein said second signal translating means comprises a second electron discharge device having a plate, a cathode and a control element, and said circuit means comprises a voltage divider circuit, one end of said voltage divider circuit being connected to said plate of said second electron discharge device, the other end of said voltage divider circuit being connected to a reference potential, and said control element of said first electron discharge device being connected to a point intermediate of said one and said other ends of said voltage divider circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,434,929 Holland et al. Jan. 27, 1948 2,435,195 Bomberger Feb. 3, 1948 2,441,387 Berger May 11, 1948 2,480,201 Selove Aug. 30, 1949 2,569,321 Liguori t Sept. 25, 1951 

